This is a Vicar brand Vl-78322 Stud. It is sold in packs of 100 pieces. These silver turnbuckle studs have single two screw base and are used for automotive, marine, and camper upholstering...
vicar vl-10393-25 stud s.s. self tapping 100 pack / Marine Fasteners
Common Sense, twist lock, Two-Screw Base
Vicar Vl-10224 Socket By Unknown Brand
Vicar Vl-10128 Button
Standard barrel length. Best for going through 1 or 2 layers of fabric only.